DESCRIPTION: Research proposed in this application seeks to identify new members of the Presenilin protein family and analyze their functions during development of the retina. The two known human Presenilins are highly related integral membrane proteins with seven putative transmembrane segments, and mutations in the two human presenilin genes are believed to account for over 90% of early-onset Alzheimer's disease. Although the biochemical activities of the Presenilin proteins are unknown, they may regulate the intracellular trafficking or processing of other proteins, such as the B-amyloid precursor protein (B-APP), which is processed to yield the major constituent of the amyloid neuritic plaques found in the brain tissues of Alzheimer's disease patients. Recently, a C elegans Presenilin protein, termed Sel-12, has been identified through genetic screens for modifiers of the Notch/Lin- 12 signaling pathway, which regulates numerous cell fate decisions during nematode development. The applicants preliminary studies have led to the isolation of a new member of the Presenilin protein family that displays 44-52% amino acid sequence identity to the human and nematode Presenilins. Specific aims of this proposal include the determination of the complete sequence and genomic organization of this new presenilin gene, the production of antibodies that recognize the encoded protein, and the isolation of mutations that disrupt the gene. Additional goals include a detailed analysis of the subcellular distribution and function of this new Presenilin in the highly polarized neuroepithelium of the developing retina. Further studies performed in mutant and transgenic retinal tissues will seek to clarify the possible involvement of Presenilin in Notch/Lin-12-mediated signaling and B-APP processing. A more long-term goal of this research is to use genetic strategies to elucidate the molecular mechanisms involving Presenilin protein activity. Screening for modifiers of Presenilin-associated phenotypes may ultimately identify interacting proteins and increase our understanding of the biochemical causes of early-onset Alzheimer's disease.